The solid waste crisis in the United States has attracted the attention of scientific, legislative, business and environmental communities. Some state legislatures have banned or are considering banning non-degradable plastics for packing, garbage bags, etc. Landfills are closing in many parts of the country. A great pressure is mounting to reduce the volume of non degradable solid waste generated by Americans. Plastics account for about 7% by weight and 18% by volume of the municipal solid waste. Current trends indicate that recycling will gradually become a major part of the solution. Waste-to-energy incineration and degradable plastics are also being considered as part of the solution. It is believed that degradable plastics alone will not provide the complete solution to the solid waste crisis. However, in specific cases e.g. agricultural mulch, six-pack beverage container carriers, disposable diapers, etc. degradable plastics offer attractive route to mitigate this problem.
Degradable plastics can be of two types: photodegradable and biodegradable. Photodegradable plastics have a structure or contain additives which promote degradation (chain scission and/or crosslinking depending on the polymer type) induced by actinic or ultraviolet (UV) radiation from the sun. Biodegradation involves the breakdown or deterioration of the polymer by microorganisms, e.g. bacteria or fungi in soil, sewage etc.
Some biodegradable polymers are already being marketed. They include poly(3-hydroxybutyrate) or PHB and the random copolymer poly(3-hydroxybutyrate-3-hydroxyvalerate) or PHBV. However, this material is very expensive, about $15/lb. Commercial development is being impeded for this reason.
Polyolefins with starch additive have also been studied for biodegradability, but only one mechanism of degradation is provided. The starch itself decomposes above about 230.degree. C., and so offers sever limitation in polymer melt processability. Other disadvantages include a sacrifice of physical properties and color, due to the presence of the starch. In state-of-the-art degradable polymers which contain additives, bio- and photodegradability inducing additives are utilized separately. A polymer/polymer blend, which takes advantage of bio- and photo-degradability as claimed herein, would have technological and commercial advantages.